The present invention relates to a constant-flow fluid controlling valve for automatically controlling the rate of flow of fluid passing therethrough to thereby maintain a constant rate of fluid flow even when fluctuations in fluid pressure take place at either the inlet or outlet side of the valve.
In a known constant-flow fluid controlling valves of the diaphragm or piston type, when fluid pressure on the inlet side increases or when fluid pressure on the outlet side decreases, increasing the rate of fluid flow through a restriction installed in a flow passage on the inlet side and also increasing the pressure differential across the restriction, the diaphragm or piston moves, moving a valve stem connected thereto to thereby reduce the rate of flow of fluid passing through the controlling valve. When fluid pressures are well balanced as described above, the following equation holds: EQU (P.sub.1 -P.sub.2).times.S=F-W
where
P.sub.1 =pressure on the upstream side of the restriction. PA1 P.sub.2 =pressure on the downstream side of the restriction. PA1 S=effective area of the diaphragm. PA1 F=pulling force of a spring exerting on the valve stem. PA1 W=sum of all the weights of an inner valve and the parts attached thereto in fluid.
The above equation can be changed into the equation ##EQU1## Since the pressure differential created across the restriction is held constant, the controlling valve is capable of sending the fluid at a constant rate of fluid flow.
However, the difference in magnitude between the upward and downward forces acting on the inner valve must be nullified, irrespective of the values for the pressures P.sub.1 and P.sub.2, in order that the above equation should be made to hold.
In other words, it is essential that a constant-flow fluid controlling valve should be designed in such a way that friction between a valve stem and the parts guiding it is reduced to a minimum and also that an inner valve is not moved up and down in a vertical line as result of pressures received directly from the fluid.
The valve of the present invention is an automatic flow controlling valve embodying such conception and thus maintaining a constant rate of fluid flow by utilizing the energy itself of the fluid flowing therethrough.